In a manufacturing process of a semiconductor device or an FPD (Flat Panel Display), a plasma is often used in the process, e.g., etching, deposition, oxidation, sputtering or the like, in order to allow a processing gas to react efficiently at a relatively low temperature. Conventionally, a capacitively coupled plasma processing apparatus is mainly used to easily realize a plasma having a large diameter for single-wafer plasma processing apparatuses.
In general, the capacitively coupled plasma etching apparatus has a configuration in which an upper electrode and a lower electrode are disposed in parallel to each other in a vacuum processing chamber. A substrate to be processed (a semiconductor wafer, a glass substrate, or the like) is mounted on the lower electrode while a radio frequency (RF) power is applied between both electrodes. Then, electrons accelerated by an RF electric field formed between the electrodes, secondary electrons emitted from the electrodes, or heated electrons collide with molecules of the processing gas to ionize them to thereby generate plasma of the processing gas, and accordingly, a desired micro-processing, e.g., an etching process, is performed on the substrate surface by radicals or ions in the plasma.
In the plasma etching apparatus, there is widely used a lower electrode dual frequency application type in which a first RF power having a relatively high frequency (normally 40 MHz or higher) appropriate for plasma generation (RF discharge) and a second RF power having a relatively low frequency (normally 13.56 MHz or lower) appropriate for ion attraction (bias) are applied to the lower electrode at the same time.
In the capacitively coupled plasma processing apparatus which realize the plasma having the large diameter, however, it has been difficult to carry out the plasma process uniformly on every position on the substrate, and this problem has been an obstacle to the enhancement of production yield.
Generally, in the plasma processing apparatus, a plasma density distribution inside the chamber tends to easily change depending on process parameters (pressure, RF power, kind of gas, and the like). Thus, although a highly uniform process result is obtained under a certain processing condition, the uniformity may be deteriorated if a processing condition is changed to obtain required processing characteristics. In fact, it is difficult to implement a chamber structure which guarantees high process uniformity under a wide range of processing conditions. Especially, in case of etching multilayer films on a substrate in plural steps consecutively, it is difficult to obtain the process uniformity with fine etching characteristics in every step because process parameters or materials of etching masks employed in each step or for each film to be processed are different.
In that regard, a conventional method of controlling an impedance of an electrode in an electric circuit to vary the plasma density distribution (see, e.g., Japanese Patent Laid-open Application No. 2004-96066 corresponding to U.S. Patent Application Publication No. 2004/0035365 A1) is not an active control method. Thus, it has been difficult to be dealt with various processes or variations in processing conditions flexibly, so that recently required high level of plasma process uniformity could not be achieved.